Piano string-frame



July 19, 1932 5, WEBER 1,867,788

PIANO STRING FRAME Filed Feb. 27, 1931 61y INVENTOR 2 /70) .A TTORIVEY Patented July '19, 1982 UNITED STATES PATENT OFFICE STANLEY WEBER, OF LONG ISLAND CITY, NEW YORK, ASSIGNOR TO STEINWAY & SONS,

OF NEW YORK, N. Y., A CORPORATION OF NEW YORK PIANO STRING-FRAME Application filed February 27, 1931. SerialNo. 518,671.

This invention relates to piano stringframes.

In the past, many attempts have been made to produce a rib, over which the piano strings pass, which will be ver hard, and yet at the same time in no way a ect the qualtiy of the tone. One of such attempts consisted in case hardening the entire casting, but during this process distortion and often rupture of the casting occurred, rendering it useless for fine musical instruments. Another attempt involved the chilling of the desired part, such as the rib, but such chilling requires machining to the exact dimensions for good piano practice and accordingly this method was found to be too difiicult and too costly. Another attempt consisted in inserting studs or hard steel ribs into thecast iron, but the bjection to this was the loss and dissipation of vibrational energy, and consequent deterioration of the tone quality.

The use of the invention is free from all of the various objections inherent in the older processes cited.

In the manufacture of piano plates or string frames an unusually large proportion of charcoal iron, usually as much as fifty per cent, is used. The castings are allowed to cool in the mold during a perlod of eight hours during which time the temperature 200 C. Upon analysis of the final casting it has been found that a large proportion, about 3 percent, (two to four percent) of carbon has separated out as graphitic carbon. The ribs of such frames were machined and the piano strings under tension would soon cut into the ridge of the rib, and in consequence the tonal qualities would be detrimentally influenced.

This invention applies for example, to an improved piano plate in which the contactual surface of the ridge of the rib is alone heat-treated. In this method of localized treatment through heating of the cast ron ridge of the rib of the plate bar or stringframe, the ridge is heated to a temperature high enough to bring about a re-solution of the carbon, graphitic or combined or both, in the metal of the ridge, and thereupon the drops from approximately 1600 C. down to,

ridge is allowed to cool comparatively rapidly. Cast-iron parts other than piano plate bars may be also treated to obtain the desired product.

To describe the invention more in detail, I proceed as follows: After the rib portion of the frame has been machined to the desired finish and dimensions, the ridge portion of the rib upon which the strings are intended to rest, is subjected to the action of heat, in the form of an electric arc, which is played along the ridge surface, using an electrode of either copper, carbon or other suitable material, and employing an electric current of high amperage of about one thousand to two thousand amperes per square inch. The electrode is passed over the edge of the ridge comparatively rapidly, to and fro, so as to avoid excessive heating or melting of the iron at any one point and also to'avoid as much as possible the heating of parts of the casting beyond or below the ridge, so that substantially only the contactual surface of the ridge with the strings is treated. It is very desirable in piano frames to maintain as much of the rib of cast iron in its original form and quality as possible. On the one hand, the entire rib should remain cast iron in order to utilize the tonal vibration deadening or inert qualities of cast iron, but on the other hand, the cutting of the strings into the ridge has the objections referred to. The satisfactory solution of the problem depends largely upon maintaining asmuch of the cast iron constituency as possible, but so treating the ridge that cutting in of the strings is prevented. Therefore, the heat is localized to the contactual surface of the ridge of the rib and to as little of the metal immediately below the surface as is practically possible. During this heating operation at such temperatures, of about 1200 to 1500 (l, the graphitic carbon in the cast iron passes back into solution so that upon comparatively sudden cooling, as results from exposing such highly heated localized portions to room temperature, after the electrode is removed, the carbon is only partially liberated again as graphite, much of the carbon being retained as carbides of iron. The 1 transformation of graphitic carbon to these carbides of iron results in an extremely hard ridge edge capable of resisting the action of the tensioned strings. Piano wire passed thereover under the tension to which it is subjected in actual use does not imbed itself into the ridge.

In the accompanying drawing,

Figure 1 represents a transverse cross section of a portion of the well known piano string frame, and

Figure 2 shows an enlarged view of the ridge of one of these frames.

In Fig. 1, the string-frame flange 10 called the front duplex scale, has a rib 11 over which the piano string 12, which is fastened to the pin 13, passes. The capo tasto bar 15 has also a rib 16 below which the piano string 12 passes. The ridges 16 and 17 of these ribs 11 and 16 are treated as described along the length over which the piano strings pass. After these ridges of the ribs have been treated as before described, a cross sectional cut thereof would closely resemble Fig. 2 which is enlarged and is diagrammatic only, to show the dilference in molecular structure of the respective parts thereof.

he process consists in locally re-heating the ridge of the rib, of a piano string-frame by bringing the temperature of the ridge to almost the melting point of the metal, and then allowing this localized heated area to cool within a period of a few minutes, instead of eight hours, as during the original manufacture of the cast iron piano plate or string frame.

Although an example of the application of the invention to piano parts has been given, it is not desired that the invention be confined, and it will be readily understood by those versed in the art that cast iron parts for purposes other than for musical instruments such, for example, as cast iron metal edges of stair treads, washers, etc. to resist wear, can be similarly heat-treated.

It may be said that the invention contemplates a cast-iron piece in which the conversion of localized portions or selected areas of high graphitic iron castings into high test gray iron 1s efiected, while allowing the 1113.]01 portion to remain as h'gh graphitic cast iron.

The ridge is modified physically and chemically, an thereby a modification of the mechanical properties is obtained, without affecting the properties of the remaining mass of the artic e. The. graphitic carbon of the rid is re-dissolved, with the formation of car ides and the retention of such carbides upon cooling, while the mass of cast iron remains in its graphitic condition. A cast 11'011 iano plate or frame so constructed is free rom distortions in shape or levels, and free from tonal vibrational ener losses.

The valuable properties of higi test gray iron are well recognized, and the same are utilized in the ridge of the rib of the frame. 9n the other hand, the valuable properties of high graphitic cast iron for piano parts are also recognized, and these are utilized in the portions other than the ridge of the frame. A divisional case of the present case has been filed on November 24, 1931, hearing Serial No. 577072 for method of making piano string frames.

"W hat is claimed is:

1. A cast iron piano plate or string frame having a one piece rib with a ridge over which the strings are adapted to pass, the ridge being integral with the body of the frame and its surface only being hardened to non-graphitic structure to resist the action of the tension of the strings, the remainingi parts of the rib and frame being untreate and of graphitic cast iron, said plate or frame being free from distortion in shape or levels and vibrational energy losses.

2. A cast iron piano plate or frame having a rib integral therewith with a string supporting ridge, said ridge having a relatively hardened-surface of heat treated metal, hardened sufliciently to resist the cutting action of the strings under tension and the remaining portion of the plate or frame being of untreated, unhardened cast iron constituency.

3. A unitary cast iron piano plate or string frame having a rib integral therewith and disposed transversely of the length of the plate, the rib having its topmost portion seectively treated to change it to a nongraphitic structure to resist cutting action of strings held under tension against said portion, while the remaining portion of the rib in the plate or frame is in an untreated heterogeneous structural condition.

4. In a piano, the combination consisting of a cast iron piano plate or frame having a rib with a ridge, a capo tasto bar havin a rib with a. ridge, said ridges being dispose with their transverse axes in parallel planes at a distance from each other, and a tensioned string passing over the ridges, said ridges having their topmost portions hardened to alter the graphitic structure of the same and render the same resistant to the cutting action of the strings while the remaining portions of said plate or frame and capo tasto are unhardened to offer resistance to the vibrations imparted thereto by the strings when actuated.

In testimony that I claim the foregoing as my invention, I have si ed my name hereto.

- ST NLEY WEBER. 

